Filament coating apparatus

ABSTRACT

Method and apparatus for coating fibers of glass and the like with a liquid such as molten aluminum. The fibers are passed through a lip of the molten metal which projects from an upper edge of a vessel which holds a body of the molten metal. The coated fibers are then passed over a heated wiper to more uniformly distribute the molten metal on the fibers before the metal hardens. An automatic control is provided for maintaining a substantially constant molten metal level in the vessel as the metal is applied to the fibers.

United States Patent Kime Dec. 25, 1973 [54] FILAMENT COATING APPARATUS 3,231,459 1/1966 Warthen 117/126 GM X 3,371,995 3/1968 Pultz [76] ihviimor 2:12- 51 1 ROme 3.507.250 4/1970 Dew, .lr 118/420 x [22] Filed: Nov. 6, 1972 Primary Examiner-Morris Kaplan [211 pp No; 303,902 Attorney-Paul F. Stutz Related U.S. Application Data 57] ABSTRACT [62] Division of Ser. No. 244,182, April 14. 1972.

Method and apparatus for coatmg fibers of glass and s2 U.S. c1. 118/420 the like with a liquid Such as when aluminum The 51 1111.01. B05c 3/176 fibers are Passed ihmigh a when metal [58] Field of Search 118/420, D16. 18 which Projects from an edge Of a vessel which s/ 19 H7, 23 124 1 7/23 2 holds a body Of thfi molten metal. The coated flbIS 232, 5 114, l 15 6 65/3 are then passed over a heated wiper to more uniformly distribute the molten metal on the fibers before the [56] References Cited metal hardens. An automatic control is provided for UNITED STATES PATENTS maintaining a substantially constant molten metal level in the vessel as the metal is applied to the fibers. 2,976,177 3/1961 Warthen 118/420 3,227,577 1/1966 Baessler et a1 118/420 X 5 Claims, 5 Drawing Figures PATENTED 05225 I913 SHEEIIOFZ CONTROL may FILAMENT COATING APPARATUS This is a division of copending application Ser. No. 244,182, filed Apr. 14, 1972.

This invention relates to fiber production and, more particularly, to an improved apparatus for coating fibers with a liquid. In a preferred form, glass fibers are coated with molten aluminum.

Radio wave reflectors consisting of random length electrical conductors are sometimes dispersed from military aircraft to confuse enemy radar and to misdirect anti-aircraft fire controlled thereby. Such reflectors are commonly known as chaf rope or window. The effectiveness of chaff against enemy radar depends upon a number of factors. While heavier metals such as zinc, tin, lead, bismuth and some alloys of these metals, such as copper and nickel, may theoretically be used in manufacturing chaff, in actual practice aluminum has been the metal chiefly employed because of its low specific gravity and its resulting capacity of relatively slow descent through the air. Another factor is the effective length of the chaff with respect to the frequency of the enemy radar. Since individual lengths or strips of chaff act as dipoles which reflect or re-radiate the radar waves incident thereon, greatest effectiveness requires a length closely equal to one-half the wavelength of the hostile radar.

Furthermore, it is necessary that the individual lengths or strands of chaff be sufficiently stiff to resist bending without breaking, and sufficiently resilient to assume or to reassume a linear form. Otherwise, if the individual lengths of chaff are easily distorted out of a linear form, as by air currents, or if they become easily entangled with one or more other strands on being launched or expelled from an aircraft, the effectiveness of the chaff in re-radiating or reflecting the radar waves, and thereby confusing enemy fire, can be greatly diminished.

In a preferred form, chaff has been formed from random lengths of glass fibers coated with an electrical conductor, preferably aluminum. Chaff of this type has been particularly effective due to the strength and resilience of the glass fibers. Even when the glass fibers are several feet long, they may be made ofa suitable diameter to impart sufficient resilience for assuming a linear form.

Aluminum coated glass fibers have other potential commercial uses. Aluminum wire, for example, is generally used for high voltage power transmission. The substitution of aluminum coated glass fibers for the aluminum wire would result in a considerable savings in the cost of materials used for manufacturing power transmission lines. Furthermore, the aluminum coated glass fibers would not stretch as annealed aluminum wire stretches.

Various methods have been used in the past for manufacturing aluminum coated fibers. One such method is shown in U.S. Pat. No. 3,544,997 wherein glass fibers are passed over a roll applicator which applies molten metal to the fibers. However, problems have occurred with this and other prior art methods. Extreme care must be taken as molten metal is applied to the glass fibers to prevent thermal stress in the glass fibers and to prevent the metal from freezing or solidifying too soon, causing the fibers to break. If the molten aluminum collects on the applicator, it acts as a heat sink and increases the probability that the aluminum will solidify and break the fibers.

SUMMARY OF THE INVENTION According to the present invention, an improved apparatus is provided for coating fibers of glass, synthetic resins, and the like with molten metal and other liquids. After the fibers are formed, and while they are still quite hot, the fibers are passed through a lip of the molten metal projecting from an upper edge of a vessel which holds a body of the molten metal. The fibers are then passed over a heated wiper to distribute the molten metal uniformly over the fibers. The fibers are then cooled, a sizing is applied and the coated fibers are collected into a suitable package.

The level of the molten aluminum in the vessel is extremely critical for maintaining a constant and uniform lip for uniformly coating the fibers. The level of the molten aluminum is sensed by means of a pneumatic probe. A wire formed of the metal from which the fibers are coated is continuously fed into the vessel at a relatively slow rate when the surface of the molten metal exceeds a desired level and at a fast rate when the surface of the molten metal is below the desired level. A level control circuit is responsive to the pneumatic probe for controlling the wire feed rate. By changing the rate at which the wire is fed into the vessel, an average feed rate corresponding to the rate at which the metal is applied to the fibers is maintained. The level control circuit also includes a safety disconnect for stopping the wire feed and energizing an alarm when the surface of the molten metal is either dangerously high or dangerously low. If the molten metal level should drop from a dangerously high level to within an allowed tolerance, the wire feed may be automatically re-initiated either immediately or after a short time delay.

Accordingly, it is a preferred object of the invention to provide an improved apparatus for coating fibers with metal.

Another object of the invention is to provide an improved apparatus for producing aluminum coated glass fibers.

Still another object of the invention is to provide improved apparatus for maintaining a substantially constant molten metal level in apparatus for applying molten metal to fibers.

Other objects and advantages of the invention will become apparent from the following detailed description, with reference being made to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic front elevational view of apparatus in accordance with the present invention for producing metal coated glass fibers;

FIG. 2 is a schematic side elevational view of the apparatus of FIG. l for producing metal coated glass fibers;

FIG. 3 is a cross-sectional view of the melting vessel for the molten metal, as taken along line 33 of FIG.

FIG. 4 is an enlarged fragmentary view showing the construction of the upper edge of the vessel for holding the molten metal and the formation of a molten metal lip; and

FIG. 5 is a schematic diagram of the electric circuit for maintaining substantially constant the level of the molten metal.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. 1 and 2, apparatus embodying the principles of the present invention is shown for producing aluminum coated glass fibers. Although a specific embodiment is shown and described, it will, of course, be appreciated that the apparatus 10 may be used for coating glass fibers with liquids and metals other than aluminum and for coating other types of fibers with liquids such as molten metals. The apparatus 10 may include conventional apparatus for forming glass fibers such as melting unit 11 having associated therewith an electrical feeder or bushing 12. The bushing 12 has in its bottom a plurality of aligned tips 13 having aligned orifices of small dimension which form the streams of molten glass from which fibers 14 are drawn or attenuated at a high velocity. The bushing 12 is made of a high temperature electrically conducting material such as platinum and is provided with terminals 15 at opposite ends thereof across which a potential is applied to supply current of a magnitude sufficient to heat the molten glass to the desired attenuating temperature.

The force of withdrawal of the fibers 14 from the molten material flowing from the bushing 12 may be provided by conventional winding apparatus, such as a winder 16. The winder 16 includes a motor (not shown) for driving a collet 17. A package tube 18 is placed on the driven collet 17. The fibers 14 may be individually wound on the package tube 18, as shown, or they may be gathered into a single strand and wound on the package tube 18. When the fibers 14 are collected into a single strand, a traverse must be provided to distribute the strand uniformly across the package 18.

Immediately after the streams of molten glass are attenuated into the filaments or fibers 14, the fibers 14 pass a vessel 19 where they are individually coated with molten aluminum. The vessel 19 is preferably of a silicon nitride ceramic which is not attacked by molten aluminum. The vessel 19 must be positioned sufficiently close to the bushing tips 13 that the fibers 14 are still hot when they are coated with the molten aluminum. A shield (not shown) may also be positioned between the fibers 14 adjacent the tips 13 to control the temperature uniformity of the tips 13 and of the molten glass streams emitted from the tips 13, to thereby control the uniformity of the diameter of the plurality of fibers 14. If the spacing between the bushing tips 13 and the vessel 19 is such that the fibers 14 have cooled appreciably, the fibers 14 are subject to a severe thermalshock when they are coated with the molten aluminum. Such a thermal shock may cause the fibers 14 to break. A spacing on the order of three or four inches between the bushing tips 13 and the application of the molten aluminum, for example, has been found satisfactory.

After the coated fibers 14 have cooled and the aluminum coating has hardened, the fibers 14 are drawn over an applicator roll 20 on a sizing applicator 21 where a suitable sizing, such as a dilute stearic acid solution, is applied to the fibers. The fibers are subsequently collected by the winder 16 on the package tube 18.

As the fibers 14 are coated with the molten aluminum, the aluminum level in the vessel 19 will tend to drop. Additional aluminum is supplied to the vessel 19 to maintain the molten aluminum level in the vessel 19 substantially constant. The additional aluminum is supplied in the form of wire 22 delivered from a spool or reel 23. An electric motor 24 operates a suitable drive mechanism 25 for forcing wire from the spool 23 through a tube 26. The tube 26 guides the aluminum wire into the vessel 19. The aluminum in the vessel 19 is maintained in a molten state, and the added aluminum wire 22 is continuously melted, by means of an oven 27 which surrounds the vessel 19. The oven 27 may consist of a stainless steel box lined with a suitable high temperature refractory material. A coating, such as aluminum oxide, is applied to the stainless steel box to prevent corrosion from molten aluminum which may come into contact with the box. A plurality of electrical resistance heaters 27a are located within the oven 27 for supplying heat to the vessel 19. The heaters 270 may be arranged for zone heatings to maintain the molten aluminum at a substantially uniform temperature across the vessel 19.

The rate at which the aluminum wire 22 is supplied to the vessel 19 is controlled by a level control circuit 28 which senses the level of the molten aluminum with the vessel 19 by means of a pneumatic probe 29. The level control 28, as will be discussed in greater detail below, controls the operation of the motor 24 for feeding the wire 22 into the vessel 19 at the appropriate rate.

Referring now to FIGS. 3 and 4, the pot or vessel 19 for holding the molten aluminum or other coating liquid is shown in detail. The vessel 19 is filled with aluminum to a desired surface level 30. The pneumatic probe 29 is positioned above the surface level 30 with an open end or nozzle 31 spaced slightly above and directed toward the surface level 30. Except for one side 33 of the vessel 19, an upper edge 34 of the vessel 19 extends above the maximum level of the molten aluminum.

The upper portion of the vessel side 33 is shown in detail in the fragmentary view of FIG. 4. The side 33 includes an upper edge 35 which is spaced below the desired aluminum surface level 30. A weir or dam 36 projects upwardly from the upper edge 35 towards the surface 30. The dam 36 has an uppermost edge 37 which is parallel to and spaced slightly below the desired surface level 30. The uppermost edge 37 may be either rounded as shown or pointed, although a rounded edge is easier to manufacture. From the dam 36, the upper edge 35 of the side 33 extends outwardly to an exterior edge 38. The exterior edge 38 must be straight and parallel to the molten aluminum surface 30 and parallel to the uppermost edge 37 of the dam 36. When the vessel 19 is filled with molten aluminum to the normal or desired surface level 30, the molten aluminum flows over the dam 36 and, through surface tension, forms a lip 39 which projects outwardly from the exterior edge 38. The lip 39 will be maintained by the dam 36, even though the molten aluminum in the vessel 19 momentarily drops below the upper edge 37 of the dam 36.

So long as the molten aluminum is maintained at substantially the desired level 30, surface tension will prevent the aluminum from flowing over the exterior edge 38. The flow of molten aluminum is further prevented by the formation of a concave surface tension recess 40 within the vessel side 33 contiguous to the exterior edge 38. immediately below the surface tension recess 40, a second recess 41 is formed in the vessel side 33. A small diameter ceramic rod 42 is mounted within the recess 41. An electric heater wire 43 is passed longitudinally through the ceramic rod 42 for electrically heating the rod 42. Electric current is passed through the wire 43 to heat the rod 42 to above the melting temperature of aluminum.

After the molten stream of glass from the bushing tip 13 is attenuated into a fiber l4 and before the fiber 14 has cooled appreciably, the fiber 14 is passed through the molten aluminum lip 39 projecting from the vessel side 33. In passing through the aluminum lip 39, the fiber I4 is at least partially coated with the molten aluminum. The coated fiber is then wiped over the ceramic rod 42 which spreads the molten aluminum over the fiber l4, increasing the probability that the fiber 14 will be 100 percent coated with aluminum. As previously discussed, the coated fiber 14 is subsequently cooled, sizing is applied to the fiber 14 and the fiber 14 is wound onto a package tube 18. It has been found that when the fiber 14 is 100 percent coated with aluminum, it will have a dull appearance. lfless than 100 percent of the surface area of the fiber 14 is coated with the aluminum, the coated fiber 14 will appear shiny. Thus, a visual examination will readily indicate when the apparatus 14) is properly adjusted for completely coating the fibers with the molten aluminum.

It has been found that the construction and the alignment of the vessel 19 is extremely critical for obtaining a 100 percent aluminum coating and for minimizing fiber breakage. If the uppermost edge 37 of the dam 36 is not flat and aligned parallel to the molten aluminum surface or if the exterior edge 38 of the side 33 is not straight and parallel to the molten aluminum surface and parallel to the edge 37, then the lip 39 will not extend uniformly across the full width of the vessel 19. In extreme cases, the molten aluminum will flow over the side 33 without forming a lip 39. If the lip 39 is not uniform and some of the fibers 14 are not coated with the molten aluminum, abrasion and tension caused by dragging the fibers over the ceramic rod 42 will cause the uncoated fibers 14 to break. In addition, both the exterior edge 38 and the heated rod 42 must be parallel to the aligned plurality of orificed tips 13 on the bushing 12.

Another difficulty occurs at times from the aluminum gauging up and freezing on the ceramic rod 42. The probability of this occurring is greatly reduced by heating the rod 42. However, this may still occur under certain circumstances. If the level of the molten aluminum in the vessel 19 is appreciably above the desired level 30, the aluminum may either flow over the exterior edge 38 onto the rod 42 or the lip 39 may project too far from the edge 38, applying too much aluminum to the fibers 14, which is deposited on the rod 42. As aluminum builds up on the ceramic rod 42, it acts as a heat sink and removes heat from the fibers l4. Eventually, sufficient heat is withdrawn from at least some of the fibers 14 to cause the aluminum to harden and the fibers 14 to break. Another possible cause of aluminum buildup on the ceramic rod 42 is from not having the vessel 19 level so that the uppermost edge 37 of the dam 36 is not parallel to the surface 30. In this case, either the lip 39 will not be uniform or the molten aluminum will flow from the vessel 19 before the lip 39 is formed.

Referring now to FIGS. 1, 2 and 5, the level control 23 for maintaining the molten aluminum at substantially the desired level 30 in the vessel 19 is shown in detail. As previously stated, a pneumatic probe 29 is positioned above the vessel 19 with an open end or nozzle 31 spaced immediately above and directed towards the normal surface level 30. The nozzle 31 must therefore be constucted from a material which will not be corroded by molten aluminum, such as aluminum oxide coated stainless steel or silicon nitride. A highly regulated constant flow of air or other gas is delivered from a suitable source (not shown) to the pneumatic probe 29. The back pressure within the probe 29 will be dependent upon the level of the molten aluminum within the vessel 19. As the molten aluminum level drops from the desired level 30, the back pressure within the pneumatic probe 29 will drop. Conversely, as the molten aluminum level increases above the desired level 30, the back pressure within the pneumatic probe 29 will increase.

The back pressure within the pneumatic probe 29 is applied to operate an adjustable pressure switch which may, for example, consist of a type 3010 l-ll-l photohelic pressure switch manufactured by Dwyer Instrument Company. As shown in FIG. 5, the pressure switch 44 is a double-pole, single-throw switch. The switch 44 is adjusted such that, when the molten aluminum exceeds the desired surface level 30, the back pressure within the probe 29 will close the switch 44. When the molten aluminum drops below the desired level 30, the pressure drop opens the switch 44.

A conventional electrical power source (not shown), such as a commercial 1 lO-volt 60 Hz. power source, is connected to a pair of input terminals 45 and 46 for operating the level control 28 and the motor 24. The input terminal 45 is connected through a main on/off power switch 47 to a terminal 48. When the switch 47 is closed to apply power to the terminal 48, a pilot light 49 is illuminated. Power is also applied to operate the motor 24 through a voltage divider consisting of a potentiometer 50 connected between the terminals 46 and 48 through normally closed contacts of a relay 51 and a pair of series connected pressure switches 52 and 53. The potentiometer 50 is set to apply a suitable operating voltage to the motor 24 for driving the motor 24 at a predetermined fast rate. When the motor 24 is operated at the fast rate, the aluminum wire 22 is supplied to the vessel 19 at a rate faster than the aluminum is applied to the fibers 14.

As the wire 22 is supplied at a fast rate to the vessel 19, the molten aluminum level will build up within the vessel 19 until the molten aluminum exceeds the desired surface level 30. At this point, the pressure switch 44 is closed to simultaneously energize a high level warning lamp 54 and the winding of the relay 51. When the relay 51 is energized, the motor is connected to receive power from the variable tap of a second potenti ometer 55 and is disconnected from the potentiometer 50. The second potentiometer 55 is connected as a voltage divider between the terminals 46 and 48 for applying a lower operating voltage to the motor 24. The second potentiometer 55 is set to operate the motor 24 for feeding the aluminum wire 22 into the vessel 19 at a rate slower than the molten aluminum is applied to the fibers 14. Thus, in normal operation, the pressure switch 44 will be periodically closed and opened as the molten aluminum level increases and decreases from the desired level 30. As a consequence of the operation of the switch 44, the average rate at which the aluminum wire 22 is supplied to the vessel 19 will equal the rate at which the molten aluminum is applied to the fibers 14.

Under certain circumstances, the molten aluminum level within the vessel 19 may become dangerously high or dangerously low. The pressure switches 52 and 53 are also connected to the pneumatic probe 29 for sensing the dangerously high and dangerously low conditions, respectively. The switch 52 is set such that it is actuated when the pressure within the probe 29 increases due to the surface level of the molten aluminum exceeding the desired level 30 by a predetermined small amount. The switch 52 should be set such that it is actuated just before the molten aluminum overflows the vessel 19 to discontinue feeding of additional aluminum wire 22 into the vessel 19. If the aluminum level should subsequently drop, the switch 52 will be released to again energize the motor 24. An optional time delay circuit (not shown) may be provided so that a short time interval occurs after the molten aluminum level drops and before the actuated switch 52 is released. lf, for example, several of the fibers 14 break, the-aluminum level within the vessel 19 may build up faster than the molten aluminum is applied to the remaining fibers 14, even though the aluminum wire 22 is fed into the vessel 19 at the slow rate. In this event, the aluminum level will build up until the switch S2 is actuated to stop the wire feed motor 24. As the molten aluminum is consumed by the remaining ones of the fibers 14, the aluminum level will drop until the switch 52 is released to turn on the motor 24 and feed additional wire 22 into the vessel 19. Thus, the apparatus will continue to operate without overflowing the vessel 19.

If, on the other hand, the vessel 19 should develop a crack or the molten aluminum level within the vessel 19 should drop appreciably below the normal level 30 for any other reason, the switch 53 will be released by a decrease in the pressure within the pneumatic probe 29. When the switch 53 is released, the motor 24 is stopped to discontinue feeding aluminum wire 22 into the vessel 19. When either the switch 52 is energized or the switch 53 is released to stop the motor 24 because of dangerous aluminum levels, a warning lamp 56 is illuminated to notify the operator of the apparatus 10.

It will be appreciated that various changes and modifications may be made in the apparatus 10 without departing from the spirit and the scope of the claimed invention. The apparatus 10 may, for example, be used with other conventional apparatus for forming glass fibers or with apparatus for forming fibers from other materials such as synthetic resins. In addition, the apparatus 10 may be used for coating such fibers with metals other than aluminum or with other coating materials which are in a liquid state.

l claim:

1. Apparatus for coating glass fibers with metal comprising in combination:

1. a vessel for holding said metal in liquid molten form,

2. means for supplying heat to said vessel to heat and maintain said metal in a molten state,

said vessel including a generally vertical wall terminating in an upper edge surface and a dam extending upwardly from said upper edge surface, said dam controlling the flow of molten metal formed in said vessel to form a lip of molten metal projecting laterally from said wall due to the surface tension of the molten metal, said lip being thereby adapted for contact by glass fibers directed to move in a generally downward path tangential to said lip to thereby pick up a partial coating of molten metal, 3. a ceramic rod located beneath said lip generally parallel with said dam and positioned for contact by said coated filaments, spreading the molten metal into full coverage of the fibers, and

4. means for heating said ceramic rod.

2. Apparatus as claimed in claim 1, wherein said ceramic rod includes an axial bore and an electrical resistance element located therein adapted to be suitably electrically energized.

3. Apparatus for applying molten metal to a vertically descending array of parallel glass fibers, said apparatus comprising:

1. a vessel adapted to contain and maintain a reserve amount of molten metal, said vessel including:

a. a marginal wall having an upper elongate surface,

b. a dam projecting upwardly from said surface,

0. an exterior edge parallel with said dam and d. a concave recess formed in the exterior surface of said wall, said recess being parallel with and below said exterior edge, and

2. a ceramic rod located beneath and parallel with said recess, said dam and recess cooperating to assist in forming a lip of molten metal overhanging said exterior edge, as metal is added to said vessel, said lip being available for pickup contact of said metal by said descending fibers to form a partial coating of said metal and said rod being located to spread said partial coating into covering relationship with said fibers.

4. Apparatus as claimed in claim 3, wherein said ceramic rod includes an axial bore and an electrical resistance element located therein adapted to be suitably electrically energized.

5. Apparatus as claimed in claim 4 which includes means for adding metal to said vessel. 

1. Apparatus for coating glass fibers with metal comprising in combination:
 1. a vessel for holding said metal in liquid molten form,
 2. means for supplying heat to said vessel to heat and maintain said metal in a molten state, said vessel including a generally vertical wall terminating in an upper edge surface and a dam extending upwardly from said upper edge surface, said dam controlling the flow of molten metal formed in said vessel to form a lip of molten metal projecting laterally from said wall due to the surface tension of the molten metal, said lip being thereby adapted for contact by glass fibers directed to move in a generally downward path tangential to said lip to thereby pick up a partial coating of molten metal,
 3. a ceramic rod located beneath said lip generally parallel with said dam and positioned for contact by said coated filaments, spreading the molten metal into full coverage of the fibers, and
 4. means for heating said ceramic rod.
 2. means for supplying heat to said vessel to heat and maintain said metal in a molten state, said vessel including a generally vertical wall terminating in an upper edge surface and a dam extending upwardly from said upper edge surface, said dam controlling the flow of molten metal formed in said vessel to form a lip of molten metal projecting laterally from said wall due to the surface tension of the molten metal, said lip being thereby adapted for contact by glass fibers directed to move in a generally downward path tangential to said lip to thereby pick up a partial coating of molten metal,
 2. Apparatus as claimed in claim 1, wherein said ceramic rod includes an axial bore and an electrical resistance element located therein adapted to be suitably electrically energized.
 2. a ceramic rod located beneath and parallel with said recess, said dam and recess cooperating to assist in forming a lip of molten metal overhanging said exterior edge, as metal is added to said vessel, said lip being available for pickup contact of said metal by said descending fibers to form a partial coating of said metal and said rod being located to spread said partial coating into covering relationship with said fibers.
 3. Apparatus for applying molten metal to a vertically descending array of parallel glass fibers, said apparatus comprising:
 3. a ceramic rod located beneath said lip generally parallel with said dam and positioned for contact by said coated filaments, spreading the molten metal into full coverage of the fibers, and
 4. means for heating said ceramic rod.
 4. Apparatus as claimed in claim 3, wherein said ceramic rod includes an axial bore and an electrical resistance element located therein adapted to be suitably electrically energized.
 5. Apparatus as claimed in claim 4 which includes means for adding metal to said vessel. 